1. Field of the Invention
The present invention relates to an electromagnetic actuating system, and particularly to an electromagnetic actuating system which actuates a valve member by cooperation of an electromagnetic force generated by an electromagnet and a resilient force generated by a spring.
2. Description of the Related Art
Conventionally, a solenoid valve is known as disclosed in Japanese Laid-Open Patent Application No. 7-335437. The solenoid valve has a valve member which is movably guided in an axial direction. An armature is connected to the valve member, and a pair of electromagnets are provided on respective sides of the armature. The armature is pressed toward a neutral position between the electromagnets by a pair of springs. When an exciting current is supplied to one of the electromagnets, an electromagnetic force is exerted on the armature in a direction toward that electromagnet. Thus, according to the above-mentioned solenoid valve, it is possible to actuate the valve member to be closed and opened by alternately supplying exciting currents to the electromagnets. In such a solenoid valve, it is desired to actuate the valve member with a high response while reducing power consumption of the solenoid valve.
It is an object of the present invention to provide an electromagnetic actuating system which can actuate a valve member with a high response while reducing power consumption of the system.
The above-mentioned object of the present invention can be achieved by an electromagnetic actuating system, comprising: a valve member; an armature which moves with the valve member; an electromagnet which attracts the armature in a direction of movement of the valve member by being supplied with a current; a spring which presses the armature away from the electromagnet; a permanent magnet which can exert a magnetic attracting force between the armature and the electromagnet; and a current controller which supplies a release current to the electromagnet so that magnetic flux is generated in a direction opposite to a direction of magnetic flux generated by the permanent magnet when the armature is released from the electromagnet. When the valve member functions as an intake valve or an exhaust valve of an internal combustion engine, the current controller may control an amount of the release current in accordance with an operating state of the internal combustion engine.
In the invention, the permanent magnet can exert a magnetic attracting force between the armature and the electromagnet. Thus, a current which is required to be supplied to the electromagnet to attract the armature can be reduced. On the other hand, the magnetic attracting force generated by the permanent magnet acts on the armature against movement thereof when the armature is released from the electromagnet. The current controller supplies the release current to the electromagnet so that magnetic flux is generated in a direction opposite to a direction of magnetic flux generated by the permanent magnet when the armature is released from the electromagnet. Thus, the magnetic attracting force against the movement of the armature can be reduced. Consequently, it is possible to improve a response of movement of the valve member. That is, it is possible to shorten a time which is required for the valve member to move from one of a fully closed position and a fully opened position to the other (hereinafter referred to as a valve transition time).
In the invention, the valve transition time becomes smaller for a larger amount of the release current since the magnetic attracting force generated by the permanent magnet is reduced to a greater extent. On the other hand, as the amount of the release current becomes larger, the power consumption becomes greater. Thus, the amount of the release current which achieves an optimum valve transition time is not identical to the amount of the release current which minimizes the power consumption of the system. In the invention, the current controller controls the amount of the release current in accordance with the operating state of the internal combustion engine. Thus, according to the invention, it is possible to achieve a valve transition time which is required in accordance with the operating state of the internal combustion engine while reducing the power consumption of the electromagnetic actuating system. When the valve member functions as the exhaust valve of the internal combustion engine, the electromagnet may attract the armature in a valve opening direction.
In this invention, the exhaust valve is opened in a situation where a relatively high combustion pressure remains in a combustion chamber of the internal combustion engine. Thus, a large electromagnetic force must be exerted on the armature in a valve opening direction so as to actuate the exhaust valve against the high pressure in the combustion chamber. According to the invention, since the permanent magnet can exert a magnetic attracting force between the armature and the electromagnet which attracts the armature in the valve opening direction, it is possible to reduce power consumption of the system when the valve member is actuated to be opened.
When the valve member functions as the intake valve of the internal combustion engine, the electromagnet may attract the armature in a valve closing direction. In this invention, a time for which the intake valve is held in a fully closed position is relatively long. Thus, electric power required to hold the intake valve in the fully closed position occupies a relatively large part of the total power consumption of the electromagnetic actuating system. According to the invention, since the permanent magnet can exert a magnetic attracting force between the armature and the electromagnet which attracts the armature in the valve closing direction, it is possible to reduce power consumption of the system when the valve member is held in the fully closed position.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.